1. Field of the Invention
The present invention relates to an electrostatic motor which generates a driving force from an electrostatic force.
2. Description of the Related Art
There has been developed an electrostatic motor in which each of a stationary member (or a stator) and a movable member is constituted by arranging a plurality of electrodes on a film-like insulating substrate, and a multi-phase AC voltage is applied to the respective sets of electrodes of the stationary member and the movable member so as to move the movable member relative to the stationary member. As compared to an electric motor using an electromagnetic force, this type of the electrostatic motor does not require a large mass component, such as a magnetic coil or a permanent magnet, and thus can be easily fabricated in a small size, which permits it to be utilized as, e.g., a drive source for a micro-machine.
Japanese Unexamined Patent Publication (Kokai) No. 6-78566 (JP6-78566A) discloses an electrostatic motor provided with a stationary member including an insulating substrate and a plurality of electrodes arranged along a major surface of the insulating substrate at predetermined intervals, and a movable member including another insulating substrate and a plurality of electrodes arranged on a major surface of the insulating substrate at predetermined intervals. In this electrostatic motor, the stationary member and the movable member are assembled together relatively movably in a direction along the major surfaces thereof, with the respective plural electrodes (usually, strip-shaped or line-shaped electrodes) being regularly opposed to each other. In this state, a three-phase AC voltage is applied to, e.g., every three parallel electrodes in the respective sets of electrodes of the stationary member and the movable member, to generate an electrostatic force between the two sets of electrodes due to traveling-wave electric fields having different phases, so that a driving force is generated in the movable member so as to act in a direction of the parallel arrangement of the electrodes (or in the direction along the major surface).
JP6-78566A also discloses a laminated configuration constructed by alternately stacking plural stationary members and plural movable members, so as to provide plural sets of stationary members and movable members, each set having opposing electrodes, for the purpose of increasing the output power of a single motor. JP6-78566A further discloses a linear electrostatic motor in which the movable member linearly moves relative to the stationary member, and a rotary electrostatic motor in which the movable member rotates about an axis relative to the stationary member.
In the electrostatic motor of the above-described type, the stationary member and the movable member, both formed as film-like members, have a small rigidity and thus are difficult to maintain their own shapes and to keep a clearance therebetween a predetermined dimension In this context, the solution has been proposed, in which a clearance is maintained by a large number of fine grains, such as glass beads, distributed between the stationary member and the movable member, as disclosed in, e.g., Akio Yamamoto, Toshiki Niino, Toshiro Higuchi, “High-Precision Positioning Control using High-Power Electrostatic Linear Drive”, Journal of the Japanese Society for Precision Engineering (JSPE), Vol. 64, No. 9, 1998, pp. 1385 to 1389.
In the above constitution wherein the clearance between the film-like stationary and movable members is controlled by fine grains, the fine grains, such as glass beads, distributed between the opposing surfaces of the stationary and movable members are interposed therebetween basically in a free state. Therefore, when the movable member moves relative to the stationary member during an operation of the electrostatic motor, the fine grains (or glass beads) tend to move accompanying thereto, which may cause the unbalanced distribution of the fine grains between the opposing surfaces. If the fine grains (or glass beads) are distributed in an unbalanced manner between the stationary member and the movable member, the clearance between the stationary and movable members may lose uniformity, and thereby the characteristics of the electrostatic motor may be varied.